An anesthetic vaporizer in which a handwheel for adjusting the metering device is locked in the zero position is described in DE-Z: Narkosemittel prazise dosieren mit Drager-Vapor 19.3 und 19.2[Accurate Metering of Anesthetics with Drager-Vapor 19.3 and 19.2], KG 5327.20/9047842 of Nov. 1, 1990, Dragerwerk AG. To turn the handwheel from the zero position, locking must first be deactivated depressing a pushbutton.
One disadvantage of this locking device is the fact that it offers protection only against inadvertent opening of the metering device, but not against opening in a state unsuitable for the operation of the anesthetic vaporizer. This is of particular significance in the case of the use of low-boiling anesthetics, whose boiling points are even below room temperature. If the anesthetic vaporizer is not cooled sufficiently, the liquid anesthetic will have partially evaporated, and putting the anesthetic vaporizer into operation would lead to highly incorrect metering. An excessively high or excessively low internal pressure, outside the normal operating pressure of the anesthetic vaporizer, would also lead to incorrect metering.